使用php和mysqli的OOP从数据库返回数据

Question

我有一个数据库php文件和一个用户php文件。 数据库是我连接数据库的地方。

<?php
    /*
     * Mysqli database class - only one connection
     */
    class Database{
        private $_connection;
        private static $_instance; //The single instance
        private $_host = 'localhost';
        private $_username = 'root';
        private $_password = '';
        private $_database = 'blogwebsite';

        public static function getInstance(){
           if(!self::$_instance){ // If no instance make one
                self::$_instance = new self();
            }
            return self::$_instance;
        }

        /*
         * Constructor
        */
        public function __construct(){
            $this->_connection = new mysqli($this->_host, $this->_username,  
            $this->_password, $this->_database);

             // Error handling
             if(mysqli_connect_error()){
             trigger_error("Failed to connect to MySQL: " .  
              mysqli_connect_errno(), E_USER_ERROR);
           }else{
               echo "You are connected to " . $this->_database;
           }
       }

        // Magic method clone is empty to prevent duplication of connection
        public function __clone(){ }

       // Get mysqli connection
       public function getConnection(){
           return $this->_connection;
        }
    }
?>

这是用户页面，我包括数据库页面。 我收到一个错误，说“未定义的变量：mysqli”和“在非对象上调用成员函数prepare（）”。

<?php
    include('class.database.php');

    class api{

       public function __construct(){
           $db = Database::getInstance();
           $mysqli = $db->getConnection();   
       }

       public function getUsername($username){
           $statement = $mysqli->prepare("SELECT username FROM users");
           $statement->bind_param('s', $username);
           $statement->execute();
           $statement->bind_result($username);
           $statement->fetch();
           $statement->close();

           return $username;
        }
    }

    $username = new api();

    echo $username->getUsername($username);
?>

任何人都可以帮助任何帮助。 非常感谢您。

Answer 1

您在类“ api”中没有“ mysqli”变量。 另外，您应该在获取Database实例之后调用getConnection() 。

class api{       
       private $mysqli;
       public function __construct(){
           $db = Database::getInstance()->getConnection();
           $this->mysqli = $db->getConnection();   
       }

       public function getUsername($username){
           $statement = $this->mysqli->prepare("SELECT username FROM users");
           $statement->bind_param('s', $username);
           $statement->execute();
           $statement->bind_result($username);
           $statement->fetch();
           $statement->close();

           return $username;
        }
    }

Answer 2

您需要创建一个局部变量$ mysql：

class api{
       protected $mysql; // <-- Here

       public function __construct(){
           $db = Database::getInstance();
           $this->mysqli = $db->getConnection();   
       }

       public function getUsername($username){
           $statement = $this->mysqli->prepare("SELECT username FROM users");
           $statement->bind_param('s', $username); // <-- what this for ?
           $statement->execute();
           $statement->bind_result($username);
           $statement->fetch();
           $statement->close();

           return $username;
        }
    }

    $username = new api();

    echo $username->getUsername($username);